Nowadays, displays such as liquid crystal displays are used in a wide range of areas including televisions for domestic purposes and displays for industrial purposes.
Referring for example to a liquid crystal display, the structure thereof is roughly divided into a liquid crystal panel, and a driving device that drives the liquid crystal panel. Conventionally, the driving device includes a plurality of image signal line driving circuits, a plurality of scanning line driving circuits, and a timing controller functioning as a control circuit that drives these driving circuits.
Each image signal line driving circuit is an integrated circuit to drive an image signal line of the liquid crystal panel. A plurality of such integrated circuits is used to drive all image signal lines of the liquid crystal panel. Likewise, each scanning line driving circuit is an integrated circuit to drive a scanning line of the liquid crystal panel. A plurality of such integrated circuits is used to drive all scanning lines of the liquid crystal panel.
The timing controller receives image data, a control reference signal according to which the image signal line driving circuits and the scanning line driving circuits are controlled, and a dot clock (DCLK) according to which process is performed. The control reference signal includes a horizontal synchronization signal (HD) functioning as a reference signal for horizontal synchronization of the liquid crystal panel, a vertical synchronization signal (VD) functioning as a reference signal for vertical synchronization of the liquid crystal panel, a data enable signal (DENA) indicating a period where image data is valid, and the like.
An image signal line driving circuit having a (built-in) timing controller has been developed recently, as disclosed in Japanese Patent Application Laid-Open No. 2010-190932. This image signal line driving circuit does not require a circuit board for a timing controller, making it possible to reduce cost for structural components. As a result, a liquid crystal display can be provided at lower cost.
A liquid crystal display includes a plurality of image signal line driving circuits having built-in timing controllers. Meanwhile, only one timing controller is required in the liquid crystal display. Thus, one of the image signal line driving circuits is used in a master mode, whereas the other image signal line driving circuit is used in a slave mode. More specifically, the image signal line driving circuit in the master mode operates based on the timing controller of the image signal line driving circuit itself, whereas the image signal line driving circuit in the slave mode operates in response to a control signal applied from the timing controller of the image signal line driving circuit in the master mode. In this case, power consumption is reduced by stopping the timing controller of the image signal line driving circuit in the slave mode.
The image signal line driving circuit having the built-in timing controller is intended for consumer use such as tablet terminals and notebook-size PCs with the intention of cost reduction, and is expected to be used in a wider range of applications such as vehicle installation.
Meanwhile, the timing controller in the image signal line driving circuit in the slave mode stops its function or performs only part of its operation as described above, meaning that the timing controller does not function effectively.